An experimental study on the CO2/sand dry-frac process

The CO2/sand dry-frac process is a waterless fracturing technology in which CO2 instead of water is used as fracturing fluid. The application of the technology abroad (in the USA and Canada) shows that it works well in stimulating low-pressure, low-permeability, strong water-locking/water sensitive reservoirs. Thus, a series of experimental studies were carried out on its production increase mechanism, fracturing fluid system, pressurized air-tight sand blender, and fracturing process. Some conclusions were made. First, the CO2 viscosity enhancement technology can raise the critical CO2 viscosity by 240–490 times, significantly improving the sand-carrying and fracture-making capacities of CO2 fracturing fluid, so it is a key technique in CO2/sand dry-frac process. Second, with the development of CO2 pressurized air-tight sand blender, a complete set of key devices for the CO2/sand dry-frac process can be made in China, meeting the requirements of the fracturing operation. Third, fully automatic flowback is also realized. Fourth, CO2 instead of water is used in this fracturing operation, saving a large amount of water consumed in fracturing, and lowering cost. Fifth, the CO2/sand dry-frac process is feasible and suitable for the stimulation of low-pressure, low-permeability and strong water-locking reservoirs, with substantial production increase.